Reverse osmosis (RO) membranes are known but there is still a need in the art for RO membranes that are resistant to degradation by halogens such as chlorine, which is often present in the feed waters of an RO process stream. There is also an ongoing need in the art for membranes with high salt rejection and flux rates.
One method of making RO membranes is by interfacial polymerization of a salt-rejecting layer on a porous polymeric support so as to form a composite membrane. See, for example, U.S. Pat. No. 4,039,440. Another method is by crosslinking polyamides or polyhydrazides having carbonyl and/or sulfonyl groups and having pendant ionic groups with metal salts. See U.S. Pat. No. 4,086,215. Meta-xylylenediamine has been condensed with trimesoyl chloride in an interfacial polymerization reaction on a polysulfone support so as to form a meta-xylylenediamide composite RO membrane. See NTIS Report No. PB83-243170 entitled "Novel Composite Membranes" by Eric K. L. Lee, et al. dated April 1983. However, the membranes so prepared were not useful for practical desalination applications due to their poor chlorine resistance and low fluxes (on the order of 6 to 10 gfd for those with salt rejections of 95% or better).